I don't know if a 556 chamber *hurts* accuracy, but I think your chances of wringing the most out of a barrel are better with a Wylde or a 223 match.
The problem with knowing for sure is that most barrels with a 556 chamber aren't set up with maximum accuracy in mind. So, it's very difficult to know for sure if differences are because of the chamber or because of some other feature of the barrel or even the rest of the gun (sights, trigger, etc).
Maybe somebody could baseline 10 Wyldes and then run 556 reamers through them and re-shoot. But my general feeling is that Wyldes work or people wouldn't use them.
I also wonder by how much the Wylde chamber helps accuracy? I've had one Wylde, and it didn't even come close to as good of accuracy as my 556 chambered rifles.. That one also had the fastest twist rate as well... My buddies RRA ATH Carbine is not nearly as accurate as any of my AR15's either, and his has a Wylde chamber. To give you an example, his averages about 1 1/4 moa, while mine all shoot around .8-.9 moa...
